Aspect Ratio & Resolution Calculator
Work out the missing width or height to keep an image or video in proportion, identify a ratio from pixel dimensions, and look up standard resolutions for every platform.
In short
Aspect ratio is width ÷ height; to resize without distortion, new height = new width × (original height ÷ original width). Standard ratios: 16:9 for video (1920 × 1080), 9:16 for Reels and Shorts (1080 × 1920), 4:3 (1024 × 768), 3:2 for DSLR photos, 1:1 for Instagram (1080 × 1080), 4:5 for Instagram portrait and 1:√2 for A4 paper.
Who this is for: Designers, video editors and web developers resizing media without distortion.
Aspect ratio basics
Aspect ratio is width ÷ height, written as two numbers (16:9) or a decimal (1.78:1). Keeping it constant when resizing means new height = new width × (original height ÷ original width). Changing it means cropping or adding bars.
| Ratio | Used for | Common sizes |
|---|---|---|
| 16:9 | Video, YouTube, monitors, TV | 1280 × 720, 1920 × 1080, 3840 × 2160 |
| 9:16 | Reels, Shorts, TikTok, stories | 1080 × 1920 |
| 4:3 | Older screens, iPad, some cameras | 1024 × 768, 2048 × 1536 |
| 3:2 | DSLR photos, 6 × 4 prints | 6000 × 4000, 1800 × 1200 |
| 1:1 | Instagram feed, profile pictures | 1080 × 1080 |
| 4:5 | Instagram portrait | 1080 × 1350 |
| √2:1 | A-series paper (A4 = 210 × 297 mm) | 2480 × 3508 at 300 dpi |
Assumptions
- Resize: missing side = known side × original ratio, rounded to whole pixels; ratio simplified by GCD.
- Identify: nearest standard ratio from a list with the percentage difference.
- Ratio mode lists common resolutions for the preset or a custom ratio.
Worked example
Ratio 4:3 → height = 1200 × 3024 ÷ 4032 = 900 px; the image is 29.8% of the original and 1.08 MP instead of 12.2 MP. To use it as a 16:9 header instead, crop to 1200 × 675 (the crop tool does this).
Frequently asked questions
How do I resize an image without stretching it?
Change only one side and calculate the other with the same ratio — enter the original size and your target width here, then use the resulting height in your editor.
Is 1920 × 1080 the same ratio as 1280 × 720?
Yes — both are exactly 16:9. 1366 × 768 is close (16:9.004) but not exact.
What ratio is A4 paper?
1:√2 (about 1:1.414) in portrait — 210 × 297 mm, or 2480 × 3508 px at 300 dpi for print.
What is the Instagram ratio limit?
Feed posts between 1.91:1 (landscape) and 4:5 (portrait); anything taller is cropped. Stories and Reels are 9:16.
How do I calculate aspect ratio from pixels?
Divide both numbers by their greatest common divisor: 1920 × 1080 → 16:9. The identify mode does it for you.
What is the 16:9 height for 1200 px width?
675 px (1200 × 9 ÷ 16).
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